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Database Migration Service (DMS): ACE Exam Study Guide (2026)

Database Migration Service

Image source: Google Cloud Documentation

1. Overview and Use Cases

Database Migration Service (DMS) is a managed, serverless service used to migrate databases to Google Cloud with minimal downtime.

  • Target Destinations: Cloud SQL (MySQL, PostgreSQL, SQL Server) and AlloyDB for PostgreSQL.
  • Migration Types:
    • Homogeneous: Source and destination are the same engine (e.g., MySQL to Cloud SQL for MySQL).
    • Heterogeneous: Source and destination are different (e.g., Oracle to Cloud SQL for PostgreSQL or AlloyDB).
  • Key Benefit: Support for continuous (online) migrations using Change Data Capture (CDC).

2. Core Architecture Components

  • Connection Profiles: Reusable configurations containing the connectivity information for the source and destination databases (IP, port, credentials).
  • Migration Jobs: The specific task that defines the source connection profile, destination instance, and migration type.
  • Private Connectivity: Ensuring secure data transfer via VPC Peering, Cloud VPN, Dedicated Interconnect, or Reverse SSH Tunnels.

3. The Migration Lifecycle

  1. Assess: Evaluate the source database for compatibility. For heterogeneous migrations, use the integrated Conversion Workspace (powered by Gemini AI) to convert schema and code.
  2. Create Connection Profiles: Define how DMS will talk to your source and destination.
  3. Define Migration Job: Select the migration type (One-time or Continuous).
  4. Run Validation: DMS performs pre-flight checks on connectivity, permissions, and configuration (e.g., binlog settings for MySQL).
  5. Start Migration: DMS performs an initial full dump and then switches to continuous replication (if selected).
  6. Promote: The final cutover step. It stops replication, disconnects the destination from the source, and makes the destination a standalone production database.

4. Source Prerequisites (Common Exam Topics)

  • MySQL: Requires binary logging (binlog) enabled and server_id configured.
  • PostgreSQL: Requires the pglogical extension (for versions < 14) or native logical replication (for versions 14+), and all tables must have primary keys.
  • Oracle (Heterogeneous): Requires supplemental logging and specific user permissions for CDC.

5. Security and Monitoring

  • Encryption: Supports SSL/TLS for data in transit and Customer-Managed Encryption Keys (CMEK) for data at rest.
  • IAM Roles:
    • roles/datamigration.admin: Full control over DMS resources.
    • roles/datamigration.viewer: Read-only access to migration status.
  • Monitoring: Integration with Cloud Monitoring to track Migration Lag (time difference between source and destination data).

6. Key Exam Tips and Gotchas

  • DMS vs. M2VM: Use DMS for Databases (Cloud SQL/AlloyDB). Use Migrate to Virtual Machines (M2VM) for full lift-and-shift of VM disks.
  • Promotion is Permanent: Once you Promote a migration job, it cannot be resumed. The destination is now the primary.
  • Primary Keys: For PostgreSQL migrations, tables without primary keys will not be replicated during the continuous phase.
  • Connectivity: If the source is on-premises, a VPN or Interconnect is highly recommended over the public internet. Use Reverse SSH Tunneling if you cannot modify firewall rules easily.

7. 2026 Updates

  • AlloyDB: Now a major target for DMS, especially for high-performance enterprise workloads.